Recent discoveries in pharmacokinetics of drugs of abuse.

Controlled human dosing studies with drugs of abuse have revealed the importance of the chosen route of administration on the delivery of drugs to the bloodstream and to their site of action. Recently, the intranasal and smoked routes have become favored by some populations for the administration of illicit drugs. Research studies with experienced heroin and cocaine users indicated that an intranasally administered drug generally provided lower blood concentrations of drug and a slower onset of action compared to the intravenous route; however, intranasal doses are easily manipulated by the user and adequate bioavailability and desired drug effects can be achieved. In addition, the trauma of needle use is avoided and disease exposure is reduced by this route. For marijuana, the smoked route of administration has always been the preferred route. In recent studies with smoked marijuana, it was revealed that single puffs of marijuana smoke produced detectable blood concentrations of tetrahydrocannabinol, the active ingredient of marijuana. Continued smoking produced rapid increases in blood concentrations with peak concentrations and effects occurring before or near the end of smoking, demonstrating the rapidity and efficacy of the smoking route for marijuana. The smoked route has also become popular with cocaine and heroin users. This route provided equivalent peak blood concentrations and time of onset of drug effects as the intravenous route. In addition, arterial boli drug concentrations reaching the brain are likely to be higher following the smoked route compared to the intravenous route. Overall, these studies demonstrated that the smoked and intranasal routes are highly efficacious for the delivery of illicit drugs and produce a similar profile of drug action to the intravenous route of administration.